In the present study, Ni-coated carbon nanotubes (Ni-CNTs) were incorporated into the Sn-Ag-Cu matrix, to form a composite solder. The interfacial intermetallic compound layer thickness formed on electroless nickel immersion gold (ENIG) metallized Cu substrate was determined under the assoldered condition. It was observed that the addition of 0.01 wt.% Ni-CNTs into the Sn-Ag-Cu solder matrix, affected the formation of intermetallic compounds during the soldering reaction. For the reaction between the composite solder and the ENIG/Cu substrate, (Cu1-xNix)6Sn5 and (Cu1-yNiy)3Sn4 were formed. The test results revealed that the thickness of interfacial IMC decreased from 2.30 μm to 1.84 μm with the addition of Ni-CNTs. Shear tests were also conducted on the as-soldered solder joints. The shear test results revealed that the composite solder joint exhibited a ~ 15% increase in yield strength and a ~ 17% increase in ultimate shear strength, as compared to its monolithic counterpart.